Role of Pneumococcal Autolysin for KLF4 Expression and Chemokine Secretion in Lung Epithelium

Abstract

In severe pneumococcal pneumonia, the delicate balance between a robust inflammatory response necessary to kill bacteria and the loss of organ function determines the outcome of disease. In this study, we tested the hypothesis that Krueppel-like factor (KLF) 4 may counter-regulate Streptococcus pneumoniae-related human lung epithelial cell activation using the potent proinflammatory chemokine IL-8 as a model molecule. Pneumococci induced KLF4 expression in human lung, in primary human bronchial epithelial cells, and in the lung epithelial cell line BEAS-2B. Whereas proinflammatory cell activation depends mainly on the classical Toll-like receptor 2-mitogen-activated protein kinase or phosphatidylinositide 3-kinase and NF-κB pathways, the induction of KLF4 occurred independently of these molecules but relied, in general, on tyrosine kinase activation and, in part, on the src kinase family member yamaguchi sarcoma viral oncogene homolog (yes) 1. The up-regulation of KLF4 depended on the activity of the main pneumococcal autolysin LytA. KLF4 overexpression suppressed S. pneumoniae-induced NF-κB and IL-8 reporter gene activation and release, whereas small interfering RNA-mediated silencing of KLF4 or yes1 kinase led to an increase in IL-8 release. The KLF4-dependent down-regulation of NF-κB luciferase activity could be rescued by the overexpression of the histone acetylase p300/cAMP response element-binding protein-associated factor. In conclusion, KLF4 acts as a counter-regulatory transcription factor in pneumococci-related proinflammatory activation of lung epithelial cells, thereby potentially preventing lung hyperinflammation and subsequent organ failure.

Adhesion and invasion of Streptococcus pneumoniae to primary and secondary respiratory epithelial cells

“…Notably, the lung-derived adenocarcinoma A549 cell line and the virus-transformed BEAS-2B bronchial cell line have been used for studying the function of virulence factors and the alterations that take place in the bacterium and the host cell upon bacteria-host interactions (3,65–68). However, the suitability of these cell lines as in vitro models for investigating the interaction between S. pneumoniae and nasal or lung mucosal cells has not been verified directly.…”

Impact of the myeloid Krüppel like factor4 during pneumococcal pneumonia

“…Zahlten et al and Herta et al have previously shown that LytA (autolysin) dependent release of bacterial DNA was a controlling factor in the induction of KLF4 in epithelial cells and macrophages during S. pneumoniae infection 167,169 . The present experiment was done to see whether the induction of KLF4 was also dependent on autolysin like in the other cell types.…”

“…KLF4 has been documented to have a role in the establishment of the skin barrier. Given that it helps in the development of skin barrier, KLF4 KO mice die shortly after birth due to spontaneous loss of body fluids 156 136,167 (see below, 3.7).…”

“…can regulate the NF-κB pathway and in turn control the cytokine profile during S. pneumoniae induced pneumonia 136,167 in human broncho-epithelial cells. While KLF4 is pro-inflammatory in myeloid cells as have been found in the present study and also has been reported earlier, whereas in the lung epithelial cells, loss of KLF4 during pneumococcal pneumonia enhanced pro-inflammatory cytokine response and reduced anti-inflammatory IL-10 secretion 136,167 .…”

Human lung ex vivo infection models

“…LytA is the major autolysin of pneumococci (Lopez and Garcia 2004) and causes the release of intrabacterial components such as PLYand bacterial DNA. Since the pneumococci-related expression of the immunomodulatory transcription factor Krueppellike factor (KLF) 4 (McConnell and Yang 2010) in human lungs seems also to depend on LytA-related pneumococcal autolysis (Zahlten et al 2015b) and as KLFs have an impact on lung cell activation in pneumococcal infection (Zahlten et al 2010(Zahlten et al , 2013(Zahlten et al , 2015a, further investigation of LytA-related activation of lung tissue is highly recommended.…”